Vacuum plasma processors for processing workpieces, such as semiconductor wafers, dielectric plates and metal plates, frequently employ coils or electrodes to establish RF electromagnetic fields for exciting gases in vacuum processing chambers to an RF plasma. The coil excitation is frequently referred to as inductive, while the electrode excitation is frequently referred to as capacitive.
The capacitively and inductively coupled vacuum plasma processors are frequently employed to etch dielectric material from a semiconductor workpiece including an underlayer and a photoresist layer. The capacitive processors have an advantage over the inductive processors because the capacitive processors cause lower damage and have higher selectivity to the underlayer and photoresist layer. The inductive processors have an advantage over the capacitive processors because the inductive processors etch workpieces at a higher rate than the capacitive processors. The inductive processors have a higher oxygen dissociation rate to enable chambers to be cleaned more rapidly than can be attained by the capacitive processors.
Hybrid processors having both capacitive and inductive RF plasma excitation have been recently introduced to perform various etch applications in the capacitive mode and efficient photoresist stripping and chamber cleaning in the inductive mode. The hybrid processors can increase processing throughput and reduce processing costs because the same chamber can be used for multiple purposes without opening the chamber or moving the workpiece from chamber to chamber to perform different processes.
Collins et al., U.S. Pat. No. 6,077,384, and WO 97/08734 disclose prior art vacuum plasma processors including both inductive and capacitive coupling wherein a ceiling of a vacuum plasma processor chamber includes a high resistivity (e.g., 30 ohm-cm, i.e., a conductivity of 0.03 mho per cm, at room temperature) semiconductor window. The semiconductor window is between the processing chamber and an insulating structure carrying a flat or domed coil. The window extends from a central longitudinal axis of the chamber to a peripheral wall of the chamber. The semiconductor window must have high resistivity, i.e., low conductivity, to prevent substantial power dissipation in the semiconductor window. If the semiconductor window has a high conductivity, the electric field component of the coil electromagnetic field dissipates substantial power in the semiconductor so power necessary to achieve plasma ignition is not coupled to the gas. Collins et al. specifically states that if the semiconductor window has a high conductivity, such as a resistivity of 0.01 ohms-cms, i.e., a conductivity of 100 mhos/cm, the frequency of the RF induction field from the coil would have to be reduced to the kilohertz range or below to couple the field the coil generates through the semiconductor window.
Collins et al. discloses a grounded non-magnetic metal Faraday shield and/or a powered or grounded non-magnetic metal backplane interposed between the semiconductor window and the coil. The non-magnetic metal backplane and Faraday shield include openings between turns of the coil and the semiconductor window so that the electric field component from the coil is coupled to the semiconductor window that extends continuously, in unbroken fashion, from the chamber center longitudinal axis to the chamber peripheral wall. The electric field components from the coil coupled through the Faraday shield and/or backplane have the same effect on the semiconductor window in the embodiments of FIGS. 25A and 37A of Collins et al. as in the embodiment of FIG. 1 of Collins et al., necessitating the use of a low conductivity semiconductor window in the embodiments of FIGS. 25A and 37A.
The semiconductor window, the backplane and Faraday shield are all made of non-magnetic material to couple the coil magnetic field components to the gas in the chamber to excite and/or maintain the gas in a plasma state. The non-magnetic metal backplane and Faraday shield openings in the backplane and Faraday shield reduce eddy current losses that occur in response to the magnetic field components.
The Collins et al. low conductivity semiconductor window has the disadvantage of applying a relatively low magnitude electromagnetic field to the plasma when the processor is operated in the capacitive mode. This is because the low conductivity silicon window does not have a high degree of electric field coupling to the plasma. Collins et al. state the semiconductor window is used for fluorine and polymerization scavenging from the plasma. The vast majority of the electromagnetic field etching which the Collins et al. device provides results from applying RF to an electrode on a chuck for the workpiece being processed.
It is, accordingly, an object of the present invention to provide a new and improved vacuum plasma processor apparatus and method for selectively, at different times, coupling plasma excitation electromagnetic fields derived from inductive and capacitive sources to gas in a single vacuum plasma processing chamber.
Another object of the invention is to provide a new and improved vacuum plasma processor apparatus and method wherein a single vacuum plasma processing chamber can efficiently perform many different processing steps and can be cleaned without being opened.
A further object of the invention is to provide a new and improved vacuum plasma processor apparatus and method wherein a vacuum plasma processing chamber can be operated to provide relatively high processing throughput, to reduce the cost of workpiece fabrication.
An additional object of the invention is to provide a new and improved vacuum plasma processor apparatus and method wherein a vacuum plasma processing chamber can be selectively operated to enable workpieces to be processed (1) during certain time periods at relatively high speeds and (2) at other times so workpiece damage is minimized, while providing high selectivity to underlayers and photoresist layers of wafers being processed.
Still another object of the invention is to provide a new and improved vacuum plasma processor including a chamber with a semiconductor plasma excitation electrode in close proximity to a plasma excitation coil, wherein the semiconductor electrode has a high enough conductivity to establish RF processing plasmas having sufficient field strength to process, in particular, etch, workpieces in the chamber.
Yet another object of the invention is to provide a new and improved vacuum plasma processor with a chamber including inductive and capacitive plasma excitation, wherein a semiconductor electrode, having high enough conductivity to establish an electromagnetic field of sufficient strength to process and, in particular, to etch a workpiece, is in proximity to a coil, but does not interact with electric field components of the electromagnetic field the coil generates and which are coupled to gas in the chamber.